1. Field of the Invention
This invention relates to the fabrication of a welded structure, especially a double shiphull bottom, comprising a pair of spaced-apart sheets of heavy sheet steel and a plurality of ribs or stiffeners interposed between and welded to said sheets. In this context, heavy sheet steel means sheet steel the thickness of which is not less than 7 millimeters. Each of the sheets referred to may be a single sheet or a composite sheet consisting of a plurality of single sheets welded together at their adjoining edges. More particularly, the invention relates to the fabrication method which includes the steps of welding one edge of said ribs or stiffeners to one face of a first one of said sheets, the other edge of said ribs or stiffeners being provided with a flange the thickness of which is substantially equal to the thickness of the second of said sheets, applying said second sheet to said ribs or stiffeners and welding it to said flanges by arc welding with a fusible electrode applied from the outside of said second sheet.
2. Description of the Prior Art
A fabrication method of the general kind above specified has been used for the fabrication of flat or substantially flat shiphull bottoms as used in barges, lighters and similar craft. In said known method, the welding of the upper sheet to the flanges of the stiffeners is carried out by the plug welding process. That is to say, the upper sheet is provided beforehand with rows of spaced oblong or circular holes in a configuration corresponding to the one of the underlying stiffeners. In the subsequent plug welding operation, said holes are filled with weld metal to form the plug welds. The extensive piercing operation, which has to be preceded by a careful marking of the hole positions, renders the method time-consuming and expensive.
It is a principal object of the invention to simplify the fabrication method above referred to in order to reduce the cost and time required. Another object of the invention is the provision of improved apparatus for carrying out the method.